The present invention relates to a discharge reaction apparatus for performing a process such as a film deposition, an etching, a cleaning, a surface hardening and the like on the surface of an object to be processed by using gas plasma generated by discharging in a vacuum.
A typical conventional apparatus utilizes a discharge by diode system. In such a conventional apparatus, for example, when the desired process is performed by disposing an object to be processed on an ungrounded electrode, if plasma density is increased by increasing electric power to be applied to the diode in order to increase the processing speed, the self-bias voltage at the ungrounded electrode becomes increased thereby strengthening ion bombardment resulting in a large damage of the object to be processed. Therefore, the upper value of the power to be supplied to the electrode is limited thereby limiting the processing speed.
In order to resolve this problem there has been proposed a process in which a magnetic field is generated in parallel to the surface of the electrode, or so as to cover the surface of the electrode. A discharge plasma with high density is generated near the electrode with the aid of this magnetic field, and the object is processed with this plasma.
In this case, as is well known, the discharge plasma is generated by a pseudo-cycloid motion which is caused by bending motion of electrons with the force of magnetic field thereby bending an orbit of the motion of the electrons and repeating a collision of the electrons to a wall of the electrode.
Typical conventional apparatus utilizing this phenomenon are shown in FIGS. 1 to 3, in which reference number 10 shows an electrode, 11 pseudo-cycloid motion of electron e, 12 magnetic line of force, B direction of magnetic field, and 13 a vacuum vessel. In FIGS. 1 and 2 the vacuum vessel is omitted.
In the pseudo-cycloid motion 11, the electron e circulates in the given direction along the surface or the periphery of the electrode 10, that is, electron e moves along and/or around the electrode 10. The direction of circulating motion is determined by the direction of magnetic field and the direction of a DC electric field. That is, the electron e circulates in the clockwise direction along tracks on the surface of the flat electrode 10 in an endless manner in FIG. 1, circulates as shown around the pillar electrode 10 in an endless manner in FIG. 2 and circulates in the clockwise direction along the inner wall of the vacuum vessel 13 and a plurality of electrodes 10 which are provided on the vacuum vessel 13 so as to cover the inner wall, in an endless manner in FIG. 3.
If the circulating motion of electrons with its pseudo-cycloid motion along the surface or the periphery of the electrode 10 is forbidden or limited and the pseudo-cycloid motion of the electrons is performed on only the desired surface of the electrode 10 as shown in FIGS. 4 and 5, the plasma with high density will be obtained and thus the process with high speed will be performed. The apparatus as shown in FIGS. 4 and 5, however, are not yet realized. In FIGS. 4 and 5, reference numeral 14 is an insulator and 15 is a barrier formed by an insulator. These insulators serve to limit or forbid the circulating motion of electrons.
The reason why the apparatus shown in FIGS. 4 and 5 are not realized is that the circulating motion of an electron is limited in one direction as described above, and if the barrier member for forbidding or limiting the circulating motion of the electron is present, the electron is collided with the barrier member resulting in a skip or jump of the electron. But the electron cannot circulate in the opposite direction and thus can only circulate in the original direction thereby staying near the barrier member so that, as shown in FIG. 6 by a plurality of dots, the density distribution of plasma 300 becomes large in gradient, that is, nonuniform and thus the process of the object subjected to this plasma becomes nonuniform.